Explain [Analyze] produces parallel scan for select Into table statements.

create table table1 (n int);
insert into table1 values (generate_series(1,5000000));
analyze table1;

set parallel_tuple_cost=0;

set max_parallel_degree=3;

postgres=# explain select into table2 from table1;

                                  QUERY PLAN                                   

-------------------------------------------------------------------------------

 Gather  (cost=1000.00..39253.03 rows=5000000 width=0)

   Number of Workers: 3

   ->  Parallel Seq Scan on table1  (cost=0.00..38253.03 rows=1612903 width=0)

(3 rows)

-----------------------------

So Explain Analyze Fails.

postgres=#  explain analyze select into table2 from table1;

ERROR:  cannot insert tuples during a parallel operation

STATEMENT:  explain analyze select into table2 from table1;

But actual execution is successful.

postgres=# select into table2 from table1;

SELECT 5000000

Reason is in ExplainOneQuery we unconditionally 

pass CURSOR_OPT_PARALLEL_OK to pg_plan_query even if query might be from

CreateTableAs/ SelectInto. Whereas in ExecCreateTableAs it is always 0.

Possible Fix:

I tried to make a patch to fix this. Now in ExplainOneQuery if into clause is

defined then parallel plans are disabled as similar to their execution.